Vacuum tube output circuit



Jan. 29, 1935. w AULL, JR 1,989,394

VACUUM TUBE OUTPUT CIRCUIT Filed May 24, 1929 5 Sheets-Sheet l /g'q- 729 PLATE VOLTAGE sounca PLATE V0 LTNE E souRgz Jan. 29, 1935. w. AULL, JR

VACUUM TUBE OUTPUT CIRCUIT Filed May 24, 1929 3 Sheets-Sheet 2 /29 1: R5 27 "W W Jan. 29, 1935. w. AULL, JR 1,989,394

VAbUUM TUBE OUTPUT CIRCUIT Filed May 24, 1929 5 Sheets-Sheet 3 Patented Jan. 29, 1935 UNITED STATES PATENT OFFICE VACUUM TUBE OUTPUT cmcurr Wilson Aull, Jr., Astoria, N. Y. ApplicationMay 24, 1929, :Serial No. 365,699

s ciaims. (01. 250-27) This invention relates to vacuum tube output in Fig. 1 and Fig. 4 shows still another practical circuits and provides a method of and means for form of .Fig. 1. I 7 coupling an ordinary vacuum tube or power tube Fig. :5 showsa practical form of the invention to an indicating device or coupling device. adapted to the output circuit of a modern radio 5 One application of my invention is to provide receiver. g

a method of coupling the power tube in a. radio Fig. 6 illustrates the application of the invenreceiver or power amplifier to the loud speaker, tion to a circuit including a vacuum tube voltand at the same time eliminate the steady 'direct meter. current from the loud speaker windings while Fig. 7 shows a practical applicatiouof he ilmaintaining a. high quality of reproduction of cuit to a modern power operated radio receiver 10 u i al o d or other reproducing equipment and 7a shows Another object is to eliminate the customary 'alcorresponding bridge c itbutput transformer or output int Fig. 8 shows another practicalcircuit some de- Another object is to reduce the manufacturing tails Of'WhiCh are different from 7, andFi cost of high quality power operated reproducing S the equivalent b i g irc i apparatus u h as power Operated radio receivers Figs. 9 and 10 are illustrations of the method Another obj t i t provide e n for slimfor both an output circuit and a coupling circuit inating the steady direct current from sensitive toa'preceding Vacuum tube in a cascadeampliindicating devices operated in plate circuits 01 both tubes receiving poweriymm the same vacuum tubes, such as vacuum tube voltmeters, sourcerelays, recorders, etc., while passing on minute In 1 I have Shown an arrangement corresig'nal operated direct c rr t flu tuations sponding in some ways with what is commercially signed t operate said indicating devices; termed a Wheatsto'ne bridgefhaving the four Another object is to provide an inexpensive bridge arms 3mm each of w c methodbf li v' tubes in amp1if1er elude various elements and c'ombinations ofele- 25 Mother is to provide method of e1im ments as hereinaiter be The Source inating the steady direct current from interstage of Plate voltage is indicated diagrammatically'at coupling transformers or choke coils, thus reducn its terminals connected 3336 d 7 between mg the likelihood or saturation and allowing the arms 1 2111012011 One Side and t arms 3 d use of less iron in such devicesrand cheapening 4, 011717116 other i 1 y 9 30 the cost consistent with a given quality of output. e indicating v ce or coupling device is To accomplish these objects 1 e t t shown diagrammatically at- 8 with its terminals ect current source'supplying plate voltage t a connected at the'points 9 and 10 between the vacuumtube from th indicating r 61 arms 1 and 3 on one side and 2 and 4 on the other I pling de i perated by Said a u tube'land for side.- In the form shown in Fig. 1 I have illus- 35 this purpose the terminals of the" indicating or trailed the Vacuum tube. 11 which may typify the other device are in effect c t d t opposite plate circuit of one or more vacuum tubes. When pairs of bridge'terminals and the powersup ly is the bridge arms 1,2, 3 and 4 are so proportioned connected between the intervening of bridge that thebridge is balanced for direct current, the 40 t r i ls, Th brid t k m y i t of bridge terminals 9-and 10 are isolated electrically 40 resistance elements, inductance elements,'capacifrom the bridge terminals 6 n q t y tive elements or combinations thereof, no direct current will flow through the indicating It should'be understood that my broad invend c ass t the b d e w s ba a c d o tion contemplates the attainment'of any one or the steady State condition W v normal filament more of the foregoing objects although I prefer voltage, plate vol ag and id biasing voltage on to design and arrange the elements to accomh v tubei V l plish all of them. v 'When the signal or other source of voltage is Referring to' the drawings, Figfl illustrates appliedto the grid of the vacuum tube,'its plate diagrammatically one arrangement by which an circuit impedance is changed," the bridge unbalindicating device, operated byavacuum tube is anced and a corresponding pulsation is applied to isolated from the-local source ofplate'voltage. the indicating device. The constants of arms2,

Fig. 2 illustrates another form," in which the 3 and 4 willdepend largely upon the type of vacsame object is accomplished, the vacuum tube 'uum tube'used and other design considerations being in another position. which will be apparent to one skilled in the art. F 59 49 mediac qn 1 h type depic ed. While I have shown a vacuum tube inbridge arm 1, it could be replaced of course by a transformer secondary, the primary of which is in the plate circuit of the corresponding vacuum tube.

In Fig. 3 I have shown an arrangement similar to that above described in which the arms 1, 2, 3 and 4 are now represented by resistances R1, R2, R3 and R4. In this case R1 and R3 each includes a choke coil which may provide all or part of the necessary resistance for the steady state bridger balancer Bridge arm- Rl; is part of the plate circuit of the. vacuum. tube 121 which: may unbalance the bridge circuit in the same general manner as vacuum tube 11 in Fig. 1.

In the arrangement of Fig. 21 have shown the of course that the filament heating source may be provided in any suitable"manner and that the grid circuit may be connected in any.- suitable manner.

. .bcorrespondszwithitheicircuit.of:Fig; 1. :It will be understood of course thatthe proper resistance relation force steady statetbalance R2 R4 The-circuit 015 Fig; 5 shows a practical application as applied to a receiving circuit includingia loud; speaker! -14.-which:takesthe. place; of the indicatingwdevice 8rbeing connectedbetweerr the tenminals 9'andl1-01, It will-be" seen that the: plate circuit of the vacuum tube 11 constitutes the arm; of. the-bridge; R2 9 includesa switch" 15. RBI nepresents-onearm 1 including. a choke: having the necessary direct current resistance. R4 includeavthe.necessary-resistance. ObviouslyFig. 5 lit-some.--respeotsresemb1esthe'normal; circuit for aloud speaker connected toa power tube except thatlhaveaddedresistancesRQ and R4-in proper proportions which combined with the resistance of the choke coil.- represented.- as R-3 and the' plate 1 .9sistance 701 the .tubeRlzforms a balance :so that the; ordinaryzcondensen usually connected with the loudispeaken 15.-1111116665591? inasmuch. as no current-willsfiow through the loudspeakerexcept whenatheobridgeis-nnbalanced by' asignal voltage applieditoltherg-ridi ofi the-tube 11.

By -thisi-arrangementr the. loud speaker condensen is; done away-, witm This isof: great advantage in high quality reproduction inasmuch as the. condenser 'ofiers a high reactance to 'low freaquenciesaascompared toithevreactance it offers-at mghw-frequenciesand consequently unless it-is of 'aiwvery large: capacity, 'isa. source. ofi distortion. Unlesaoflhigh grade the condenserwisralso a source 101-: troublevinasmuch as it-is subjectedl to high yoltagesandmay'break down completely,:

. Fligufisshowswthe principle of Fig. 4 asapplied toiawacuumrtube voltmeter? in which the bridge ari'ns-iR-1-,-; .R 2;- R3.and R4: are shown-in a manner similarl-tmthosg offFig. .5-,-.resistance2 R3 being-the direct; current--resistance: ofqathe choke. coil -or 'gtherrimpedance 16.; Vacuumtube ll may have itsi-glid bias adjustedso-thatit functions as a plate rectifiera :This adjustment may be made by potentiometer 17 by means of which an adjustablemegative grid. bias-.-may.--be fed to the grid of tube; 11 ithrough=g-rid-.1eak1$. After this adjustment-vhasrbeen made-.the gbridge arms should be adjustedior zero. current on the indicating meter adjustment may easily be effected by letting R41bean adjustable resistance.-- The other bridgeiarmssmaygbefixed-in:value. Switch 19 is diagrammatic in -practice it 1 could "be combined withrtheflii battery switch. In general this vacuum tube voltmeter may be operated in a manner similar to that described in U. S. Patent 1,232,919 issued to R. A. Heising. In my arrangement, however, I have included condensers 20 and 21 to which input terminals 22 and 23 are connected.

Another simple method of operation consists in calibrating the indicating meter 19 in volts with a given vacuum tube after the bridge has been balanced; by means of .the grid bias;adjustment 127=or-the=:.equivalent. Thereafter before using the instrument it is only necessary to adjust the bnidge until the meter reads zero on the calibrated scale.

' Tlius sourcesof voltage of any frequency may bea'measurew even though the external circuit is not closed inasmuch as the input circuit of vacuum' tube- -1*1' isso arranged that the grid biasing is independent of the source of voltage being measured as long as this voltage is within the lim- Iitsaof: the vacuuma tubeevoltmeter;

' This: methoidi forcaa vacuumitubezvoltmeterehas :someradvantagessover ithe: usualmethod inasmuch as the. device maycbeaoperatedrona'steepen portion ofi-the: gtid-l-voltage: plate-current (characteristic,

giving:.:greater"sensitivityi and in: addition, allows the; use of'sensitive direct current-indicatingin- 'struments-z for. measuring alternating currents ;of

frequencies; In1a similar: manner; othersensitivedirectcurrent indicating instruments may-be: operated-;by alternating :currents-.-. thus obtaining the. sensitivity of direct current instruments on alternating currents.- For instance thezmicroammeten 19 ofiFig. 6,-maybereplacedby a-direct current relay sensitive :BIIOllghr tor give a positive indication .when SUDDHGdvWithFfirVGIYfBW micro-amperes of 'directecurrent. This-would not; be possible. if the steady state.-directicurrent. were not: balanced :out asthe. normal plateeflow would. not only operate but; possiblyr-.-bur,nouttthe winding Obviously a filter or, vtransformer.- vwould=notqsufiice as Falternating -,cun:en t onlyv would; be passed, whichiof courselwould =-n0tgoperate-a direct current instruments- In short,-:this .output circuit, may beaused in; connection r withr-avacuum tube: .in (any: case where it- :is desired-to=utilize-- the weak gpulsating direct currenttwithout, the'presence oi thCQIBlflr tively:greatrsteadyrstatedirect currentifiowing in theplate-circuitsv g I j -Fig.,'7'-shows.-thegeneralvarrangement of; Fig. 5 applied to aamodern; power. operated amplifier system .in .whichthe source .of plate voltage which may .be from. direcflcurrent. lighting mains ..ora rectifier systemied, by alternatingcurrent. lightingmains-is'applied.to points'23 and-24 which are the input -.terminals of; a: filter comprising filter condensersr25 and:26and choke,coil 27. The customary voltage divider28 is furnished as shown to which may be connected the customary: voltage taps ,for feeding the amplifierplates; and grid biases. Inwthesnormal system choke icoil, R3 would be connectedas shown, and the loudspeaker rinseriesuwithnthe customary blocking, condenser 9 connected. However, I- have done away with .the. -blockingi condensen by connecting; the loud speaker terminal which would ordinarily'go to v the filament; circuit to .point. 10 on-the ,voltage divider thus forming the bridge-circuit, the-arms R1, R2, .R3l an'd R4. of which. I haveindicated on thediagraml .In actual operation, it axmilliammeter beinsertedin .wire 39and point lobeprogressively moved from; near 9 point '7, taking care not to burn out the loudspeaker winding, a large u r n wq g e sh w mnf he mil ammete rtt current will gradually decrease until point is reached when no current will be indicated. If the wire be progressively moved further the current in the milliammeter will reverse in direction. Thus, by my invention, the usual condenser, a source of distortion and trouble, is done away with entirely and at no additional practical cost, in most cases, in fact, at a saving in cost.

In practice, of course, the usual impedance adjusting transformer may be connected to the loud speaker as shown in one of the diagrams. Fig. 7a. shows the corresponding bridge circuit utilized in Fig. 7 together with the usual method of obtaining grid bias for the output tube 11.

Fig. 8 shows another loud speaker arrangement by which the steady direct current is eliminated from the loud speaker or transformer windings but another method of grid biasing is used. This also is a common method of obtaining the grid voltage, the corresponding grid circuit for which is shown in Fig. 8a.

My system is of advantage even when the loud speaker is connected through a transformer inasmuch as much less material is used in the transformer when the heavy direct current is balanced out inasmuch as the core cannot become saturated, which allows the use of a smaller core thus giving great saving in iron, copper and weight.

Fig. 9 includes the output circuit of Fig. 7 in which the direct current is balanced out of the loud speaker and shows in addition the direct current also balanced out of coupling transformer 32 by adjusting connection 33 on voltage divider 28. Thus the same voltage divider functions as arms R2 and R4 in two different bridge circuits. The corresponding bridge circuit together with the method of biasing the grid for the output of tube 11 as well as tube 34 is indicated in Fig. 7a.

In Fig. 10 I have indicated another circuit in which the output circuits of two vacuum tubes included in a cascade amplifier are treated by my method. Likewise any number of stages of amplification could be similarly treated.

Fig. 10 difiers from Fig. 9 particularly in the method of biasing the grids of the two vacuum tubes and the corresponding bridge circuit is similar to that shown in Fig. 80.

It will be understood that the general circuit arrangements may be varied within wide limits and that I have shown certain more or less well known circuits as typical examples.

I claim:

1. In the output circuit of a vacuum tube, four impedances at least one of which has a high inductive reactance to resistance ratio connected in series with the two outer ends joined together forming a closed bridge network, said bridge inductive reactance having a vacuum tube filament connected to it, the other end of said reactance being connected to the plate of said vacuum tube, a source of plate supply connected between the bridge junction to which the filament is attached and the bridge junction farthest removed electrically, a load device connected between the bridge junction to which the vacuum tube plate is attached and the fourth bridge junction, and means for so proportioning the bridge impedance arms that under normal conditions, substantially no direct current potential exists at the load terminals unless a change occurs in the grid circuit of the vacuum tube, and means for adjusting the biasing voltage of the grid of said tube.

2. In a vacuum tube output circuit, a bridge having arms comprising two resistance elements, the anode circuit of a vacuum tube and a choke of substantial alternating current impedance and of known resistance, a source of plate voltage supply connected at opposite junctions of the bridge and a load connected between intervening elements of said bridge so that substantially no direct current flows therethrough when said vacuum tube has zero input.

3. In a vacuum tube output circuit, a bridge having arms comprising two resistance elements, the anode circuit of a vacuum tube and a choke of known resistance, a source of plate voltage supply connected at opposite junctions of the bridge and a load connected between intervening elements, one arm of said bridge including'the plate circuit of a vacuum tube and said bridge being so balanced that said load has substantially no direct current flowing therethrough until the input circuit of said vacuum tube is excited said choke having a substantial alternating current impedance.

WILSON AULL, JR. 

